Extensive studies on the subcellular pathophysiology of ischemia in vivo and in vitro in diverse tissues have documented morphological and functional events leading to irreversible cell damage, events which may be related to alterations in the transport of diffusible ions across cell or organelle membranes. The proposed experiments will test the hypothesis that translocation and redistribution of physiologically important ions occur at the subcellular level which parallel loss of ultrastructural integrity during selected conditions simulating the in vivo ischemic process. The experimental model to be used--embryonic chick myocardial cells in culture--offers the unique ability to study, singly or in combination, factors which contribute to ischemic injury, such as active transport inhibition, hypoxia, metabolic deprivation, and acidosis. Techniques of analytical transmission electron microscopy including cryopreparation and energy dispersive X-ray spectroscopy will facilitate location and quantitation of the ions Na plus, K plus, Ca++, Mg++, and Pi within subcellular regions 10 to 20 nM in diameter. The ionic composition, ultrastructural integrity, spatial morphology and morphometry of myocardial cells will be monitored as the preparations are a) acutely or chronically exposed to ischemic conditions, and b) challenged to adapt and/or to recover following either acute or long term exposure. The ability to study in isolation individual morphological, physiological, and biochemical factors contributing to the ischemic process is unique to the cultured heart cell model. Coupled with electron probe localization and quantitation of elements within subcellular compartments, the model will enable the assessment of the role of ionic shifts in irreversible cell damage, particularly the role which structural damage may play in altered ionic compartmentation. The importance of determining the mechanisms responsible for cell injury lies in the potential for manipulation of these events, and subsequently the development of appropriate clinical interventions for control and prevention of ischemia-related diseases such as myocardial infarction.